A current trend in the design of electrical systems is to modular system configurations wherein individual electrical units of the system are readily accessible and in some cases customer removable. The use of modular designs provides a number of different advantages. Manufacture and assembly is made simpler in that each unit can be manufactured and tested separately before being assembled in the complete system. Furthermore, if a removable unit becomes defective, it can be readily removed for repair and replaced with a working device. A typical multi-component system of this type is a computing system in which data storage devices, processing hardware, power supplies and cooling fans are contained within a single support structure.
Although ease of removability of individual devices is facilitated using a modular configuration, the removal and replacement of a device usually requires the system to be closed down thus reducing the amount of time for which the system is available. It would be desirable if a defective device could be removed and replaced while the system continued to function. In order to achieve this the system design should permit easy access to removable devices while at the same time ensuring that the system "life support" functions, e.g., cooling and power continue to operate. Taking the example of a disk file data storage system comprising removable disk files and associated power and cooling units, such systems are currently available which allow for the replacement of one or more of the disk files while maintaining operation of the remaining disk files. However, removal and replacement of a failed cooling fan or power supply generally necessitates the shutting down of the whole system.
It is increasingly common that such modular systems are required to conform to a industry standard size in order that they fit within a larger data processing system. In the case of disk file storage subsystems, one challenge faced by the designer of the subsystem power and packaging is to achieve a high packaging density within the available space in order to provide a high value for the ratio of megabytes to unit volume.
The designing of a system which allows easy replacement of system subassemblies with continued system availability and high subassembly packaging density is an ongoing problem and one which is difficult to achieve in practice.